This application is based on Application No. 2000-372506, filed in Japan on Dec. 7, 2000 and Application No. 2001-183521, filed in Japan on Jun. 18, 2001, the contents of which are hereby incorporated by reference.
This invention relates to an electric fuel pump disposed within a fuel tank for a vehicular internal combustion engine for pumping fuel within the fuel tank to the engine.
FIG. 7 is a longitudinal sectional view of a conventional electric fuel pump disclosed in Japanese Patent Publication No. 7-3239, for example, and FIG. 8 is a graph showing the performance of the conventional electric fuel pump.
In these figures, an electric fuel pump comprises a pump casing assembly 1 that comprises a pump casing main body 2 and a cover 3. The pump casing assembly 1 accommodates an impeller 4 which is a disc-shaped rotary member having a row of vanes 5 disposed along the outer circumference. An arc-shaped pump flow path 7 is formed to extend along the row of the vanes 5 of the impeller 4 and to straddle between both of the pump casing main body 2 and the cover 3. The cover 3 is provided at a position corresponding to one end of the pump flow path 7 with a suction port 8 that extends from one side of the impeller 4 to open downwardly as viewed in FIG. 7, and the pump main body 2 is provided with a discharge port 9 that extends from the other side of the impeller 4 to open upwardly as viewed in FIG. 7.
The impeller 4 has inserted into its center a central shaft 6 of a rotor 16 of an electric motor 15, the rotor 16 being rotatably supported at the central shaft 6 by a bearing 17 and a bearing 18 disposed in the pump casing main body 2 and the bracket 24, respectively.
An end cover 19 made of a molded thermoplastic resin, for example, is connected to the pump casing assembly 1 through a cylindrical yoke 20 of the electric motor 15. Permanent magnets 25 are circumferentially arranged on the inner circumference of the yoke 20 and the rotor 16 is disposed inside of the circumferentially arranged permanent magnets 25.
Defined between the pump casing assembly 1 and the end cover 19 and within the yoke 20 is a fuel chamber 21 for accommodating the fuel discharged from the discharge port 9. The fuel chamber 21 is communicated with a fuel exhaust port 23 defined in the end face of the end cover 19 through a check valve 22 disposed in a communicating passage for restricting the flow direction of the fuel. A feed brush 27 is disposed for supplying an electric current to the windings of the rotor 16 through a commutator 26.
In the conventional electric fuel pump having the above-described structure, when an electric current is supplied to the windings (not shown) of the rotor 16 of the electric motor 15 through the feed brush 27 and the commutator 26, the impeller 4 is driven to rotate clockwise direction (as shown by an arrow in FIG. 8) to cause the fuel to be suctioned from the suction port 8 into one end of the pump flow path 7 and increased in pressure as it flows through the pump flow path 7 in the clockwise direction. Then the fuel enters into the fuel chamber 21 from the discharge port 9 at the other end of the flow path 7 and flows through the check valve 22 and finally discharged from the discharge port 23.
The performance (shown in FIG. 9) of the electric fuel pump can be represented by a characteristic diagram expressed by the pressure (P) of the fuel discharged from the electric fuel plotted against the axis of ordinate and the discharge amount (Q) of the fuel discharged from the electric fuel pump and the electric current (I) consumed by the electric fuel pump plotted against the axis of abscissa. The fuel discharged from the fuel discharge port 23 of the electric fuel pump is supplied to the vehicular internal combustion engine (not shown) after it is regulated to a predetermined pressure (P1) by an unillustrated pressure regulator.
It is to be noted that the pressure regulator (not shown) is a separate structure independent from the electric fuel pump as disclosed in Japanese Patent Laid-Open No. 8-177681. In such the arrangement, when the fuel discharged from the fuel exhaust port 23 of the electric fuel pump is regulated in fuel pressure by a fuel pressure regulator to P1 (shown in FIG. 9), the electric fuel pump operates continuously at a discharge rate of Q1 and at a consumption current of I1. An excessive amount of fuel Q1xe2x88x92q, which is a fuel amount that was discharged from the pump at the discharge rate Q1 but would not be consumed by the engine operated at a fuel consumption rate q, is not supplied to the engine but fed back to the fuel tank from the pressure regulator.
As has been described, the conventional electric fuel pump is arranged such that it always supplies a fuel amount of Q1 including the excessive fuel amount that is required by the engine q, so that the current consumption I1 of the fuel pump is large. Therefore, a large load is imposed on a battery of the vehicle and the fuel amount discharged from the fuel pump is decreased because some of the fuel evaporates within the pump due to the Jourl""s heat generated at the windings of the rotor 16.
Accordingly, an object of the present invention is to provide an electric fuel pump that is free from the above problems of the conventional electric fuel pump.
Another object of the invention is to provide an electric fuel pump in which the pump can be operated at a small current corresponding to the fuel consumption of the engine, thus decreasing the load on the battery, preventing the decrease of the fuel discharge amount due to the evaporation of the fuel by the Jourl""s heat at the rotor windings.
With the above objects in view, the present invention resides in an electric fuel pump comprising a pump casing assembly having a fuel inlet port and an outlet port and a rotary member driven by an electric motor disposed within the pump casing assembly for sucking fuel from the fuel inlet port and discharging it from the outlet port. A fuel discharge port is disposed for supplying the fuel discharged from the outlet port to an internal combustion engine, and a pressure regulator is disposed for regulating the pressure of the fuel to be discharged from the fuel discharge port. The pressure regulator regulates the pressure of the fuel discharged from the fuel outlet port by returning the fuel to the vicinity of the inlet port when the pressure of the fuel discharged from the outlet port is equal to or higher than a predetermined pressure.
The pressure regulator may be disposed within a regulator receptacle hole of the pump casing assembly.
The pressure regulator may comprise a valve for controlling the flow rate of the fuel to be returned to an area in the vicinity of the inlet port on the basis of the pressure of the fuel discharged from the outlet port, a spring for determining the pressure at which the valve is opened and closed, and a spring holder for holding the spring.
The electric fuel pump may further comprise an elastic member disposed on the surface of the valve which abuts against a main body of the pump casing assembly.
The valve may comprise an elastic member having an engaging projection portion and a spring receptacle having an engaging recess portion, the engaging projection portion being fitted into the engaging recess portion to join the elastic member and the spring receptacle into an integral structure.
The spring may comprise a coil spring, one end of which being fitted onto the valve and the other end of which being fitted into the spring holder to join the elastic member and the spring receptacle into an integral structure.
The spring holder may be secured at a predetermined position in the inner circumferential surface of a bore for accommodating the pressure regulator.
The spring holder may have a notch formed at its circumferential edge portion.
The rotary member may be an impeller having vanes at its outer circumference.
The electric motor may comprise a rotor having inserted therein a central shaft that engages with the rotary member, a bearing for rotatably supporting the central shaft, a pair of permanent magnets concentrically disposed at the outer circumference of the rotor and a commutator and current feed brush for supplying an electric current to a rotor winding.